Messages in this thread | | | Date | Wed, 27 May 2009 14:00:01 +0900 | From | Daisuke Nishimura <> | Subject | Re: [RFC][PATCH 2/5] add SWAP_HAS_CACHE flag to swap_map |
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On Wed, 27 May 2009 13:36:29 +0900, KAMEZAWA Hiroyuki <kamezawa.hiroyu@jp.fujitsu.com> wrote: > On Wed, 27 May 2009 13:02:46 +0900 > Daisuke Nishimura <nishimura@mxp.nes.nec.co.jp> wrote: > > > > @@ -1067,21 +1113,21 @@ static int try_to_unuse(unsigned int typ > > > } > > > > > > /* > > > - * How could swap count reach 0x7fff when the maximum > > > - * pid is 0x7fff, and there's no way to repeat a swap > > > - * page within an mm (except in shmem, where it's the > > > - * shared object which takes the reference count)? > > > - * We believe SWAP_MAP_MAX cannot occur in Linux 2.4. > > > - * > > > + * How could swap count reach 0x7ffe ? > > > + * There's no way to repeat a swap page within an mm > > > + * (except in shmem, where it's the shared object which takes > > > + * the reference count)? > > > + * We believe SWAP_MAP_MAX cannot occur.(if occur, unsigned > > > + * short is too small....) > > > * If that's wrong, then we should worry more about > > > * exit_mmap() and do_munmap() cases described above: > > > * we might be resetting SWAP_MAP_MAX too early here. > > > * We know "Undead"s can happen, they're okay, so don't > > > * report them; but do report if we reset SWAP_MAP_MAX. > > > */ > > > - if (*swap_map == SWAP_MAP_MAX) { > > > + if (swap_count(*swap_map) == SWAP_MAP_MAX) { > > > spin_lock(&swap_lock); > > > - *swap_map = 1; > > > + *swap_map = make_swap_count(0, 1); > > Can we assume the entry has SWAP_HAS_CACHE here ? > > Shouldn't we check PageSwapCache beforehand ? > > > > IIUC, in this try_to_unuse code, the page is added to swap cache and locked > before reaches here. But....ah,ok, unuse_mm() may release lock_page() before > reach here. Then... > And the owner process might have removed the swap cache before we take the lock, as the following comments in try_to_unuse() says.
> if (PageSwapCache(page) && swap_count(*swap_map) == SWAP_MAP_MAX) > > is right ? (maybe original code, set to "1" is also buggy.) > Reading the following code in try_to_unuse(), I think
int valid_swap_cache = !!(PageSwapCache(page) && page_private(page) == entry.val) : *swap_map = make_swap_count(0(or 1?), valid_swap_cache);
might be better.
But I can't confirm it anyway. I've never hit SWAP_MAP_MAX.
Thanks, Daisuke Nishimura.
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